1. Field of the Invention
This invention relates to a method of detecting a tightly adhering state, a method of controlling tight adhesion using the detection method and a method of near filed exposure as well as to a device for detecting a tightly adhering state, a device for controlling tight adhesion using such a detection device and an apparatus for near field exposure.
2. Related Background Art
Semiconductor elements of electronic devices have been intensely required to be micronized in recent years to meet the demand for compact and low-profile electronic devices. For example, the design rules currently applicable to patterns of masks and reticles are intended to achieve line and space (L&S) of 130 nm on a mass production basis. This value is expected to be reduced further in the future.
Projection aligners (exposure apparatus), which have been in the mainstream in recent years, comprise an illumination optical system for illuminating a mask, utilizing a flux of light emitted from a light source and a projection optical system arranged between the mask and the object of exposure. In such a projection aligner, the limit for achievable resolution is generally believed to be substantially equal to the wavelength of the light source involved. It is difficult to form a pattern of 0.10 μm or less by means of a projection aligner if an excimer laser is used.
Additionally, if a light source for a shorter wavelength is found, light to be used for exposure with such a short wavelength cannot pass through the optical material used in the projection optical system (namely, the vitreous material of the lenses) so that consequently it cannot project light onto the object of projection and hence the latter cannot be exposed to light.
To cope with the problem, exposure apparatus realized by using the principle of scanning near filed microscopes (SNOMs) have been proposed in recent years as means for micro-processing with dimensions of 0.1 μm or less.
For example, U.S. Pat. No. 6,171,780 proposes an apparatus for exposing a local area of dimensions exceeding the wavelength of light of an object of exposure, which is resist, to near field light that seeps out of a micro-opening pattern of 100 nm or less formed on the surface of a mask that is elastically deformable along the normal line of the mask surface, while forcing the mask to tightly adhere to the resist.
However, if an exposure operation is conducted in such a near field exposure apparatus in a state where the elastically deformable mask does not tightly adhere to the object of exposure and separated from the latter to a region where near field light is not found, it is no longer possible to expose a local area of dimensions with more than the wavelength of light of an object to light. Therefore, a near field exposure apparatus adapted to expose an local area of an object of exposure to light in a state where a exposure mask is tightly adhering to the object requires to be provided with a means for ensuring that the exposure mask is tightly adhering to the object of exposure.
Techniques that can be used for observing a displacement of an exposure mask include one that is used for X-ray aligners and with which a laser beam is irradiated onto the exposure mask and observing the displacement of the reflected beam and one with which the displacement of an exposure mask is observed with an interferometer. However, since known exposure methods were devised for the purpose of exposing an object of exposure in a state where the object of exposure, which is photoresist, is separated from a photomask and therefore any technique for detecting if the photomask is tightly adhering to the object of exposure was not considered for them.